The rotameter is a type of flowmeter used for measuring the discharge or flow rate of fluids. It is a simple and reliable device that operates on the principle of variable area flow measurement. The rotameter consists of a tapered glass or plastic tube with a float inside that moves up and down depending on the flow rate of the fluid.

Principle of Operation:
The rotameter operates on the principle of variable area flow measurement. As the fluid flows through the tapered tube, the cross-sectional area decreases, causing an increase in the fluid velocity. This increase in velocity results in a pressure drop across the tube, which causes the float to rise. The position of the float is directly proportional to the flow rate of the fluid. The higher the flow rate, the higher the position of the float.

Measurement of Discharge:
The rotameter is primarily used for measuring the discharge or flow rate of fluids. The position of the float inside the tapered tube indicates the flow rate of the fluid. The rotameter is calibrated in terms of the flow rate, and the scale on the tube allows direct reading of the flow rate.

Advantages of Rotameter:
1. Simple design and easy to install.
2. Wide range of flow measurement capabilities.
3. Suitable for both liquid and gas applications.
4. Can handle a wide range of fluid temperatures and pressures.
5. Low pressure drop across the meter.
6. Can be used for both high and low flow rates.
7. No external power source required for operation.

Limitations of Rotameter:
1. Accuracy is affected by changes in fluid viscosity and density.
2. Limited accuracy and precision compared to other flow measurement devices.
3. Not suitable for highly viscous fluids.
4. Susceptible to damage if exposed to high-pressure or high-velocity flows.
5. Fluid must be clean and free from solid particles that might obstruct the flow.

Applications of Rotameter:
1. Chemical and petrochemical industries.
2. Pharmaceutical and food processing industries.
3. Water treatment plants.
4. HVAC systems.
5. Laboratory experiments and research.
6. Oil and gas industries.
7. Industrial process control systems.